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Yea, I probably could have been a little more diligent about finding a company who does more thorough testing. Every time I complained, we attributed poor performance to flex duct temperature losses. Summer of 2010, the owner of the company responded: "I really dont see any issues with your system and spoke in-depth with my technician and he said it was on the money."

Of course, the thing that was on the money was the subcooling and superheat values. This seems to be a good example of - don't rely on just those values to determine if everything is working ok.

I finally started taking a better readings at the appropriate locations before and after the evaporator, started doing BTU calculations, and was able to prove that something wasn't right. Funny thing, this company still hasn't taken their own detailed return/supply temperature measurements - they are taking my numbers and passing it on to Carrier.

And I can't blame just this company, I did call someone else to get another opinion (last summer I believe). This was the guy that punched a hole in the return flex duct, took a quick measurement, compared to supply temp at nearest register and said everything was fine. I realized at this point, that this larger, Carrier dealer was not going to be able to help either.

Will post another update when I have one.

Originally Posted by mark beiser

This is sad.
I just realized that you posted about the poor performance of this system just over 2 years ago, and it still isn't fixed...

For the record, I said the compressor wasn't working at full capacity in 2nd stage 2 years ago when you first posted about it.

Another update, and hopefully we are moving in the right direction. Finally got the Carrier service rep out here, and I was impressed - he definitely seemed to know his stuff.

He said that I need that 4" spacer between the furnace and the N coil. Even though the two are matched sizes, he said that Carrier now recommends that spacer, especially in larger systems (4 ton in my case). He said at hi stage, there really isn't enough room for air to exit the heat exchanger, and then flow into that right leg of the N coil. He said this was now in the CNPVP coil installation instructions (although I couldn't find anything in the instructions that specifically said that).

He acknowledged that I've really had this problem since day 1 (July 2007). I just could never prove it until I did my own BTU calculations.

OK, here is the latest on this issue. Based on the info my local HVAC contractor passed to Carrier, Carrier concluded the TXV was bad. It was just in the 5 year parts warranty, so Carrier paid the cost of the TXV (I actually paid the difference and had the entire evaporator replaced with a newer aluminum Carrier N coil). No need going through all that and then have the evaporator leak in a year or so.

At any rate, made no difference at all, and I knew 10 minutes after they fired it back up. Same symptons:

1) Supply air temp goes up 5-10F from low to high stage

2) Delta T, measured at the evap is 10-14F in high stage, good 20 or so in low stage

3) Suction pressure always goes up about 10psig from low to high stage, head pressure essentially doesn't change. Local tech says Carrier told him this was OK, although the Carrier application and service guide for the 24ANA7 reads: "Suction pressure should be reduced by 5--10% when switching from low to high capacity. There should be a 10--20% increase in liquid pressure when switching from low to high capacity."

4) When I take careful and repeated wet bulb/dry bulb return/supply temps at the appropriate locations near the evaporator BTU calculations are essentially unchanged from low to high stage. (I've posted figures here before - no need to post them again - they didn't change)

Now, before Carrier agreed to replace the TXV, they did have the local tech come back out an check compressor amp draw (because he neglected to do that on the first visit). On a super hot day it was 6A low stage and just over 9A hi stage. Again, the Carrier service guide reads: "Compressor current should increase 100--250% when switching from low to high stage.", but this apparently didn't throw any red flags for the Carrier service rep, so they went with a TXV replacement

At this point, I'm waiting the local HVAC company to get a response from Carrier on the next step. I figure I probably have a good case. Carrier didn't agree to do an in-warranty TXV replacement if they didn't think something was wrong, and since the symptons have not changed, I wouldn't think that they could now say everything is OK. I still think its that Bristol TS compressor.

Here is my question: If I hit a dead end here, can I go directly to Carrier Mid Atlantic and start working this issue myself? Does Carrier have service reps that respond to things like this, rather than going through a local HVAC contractor?

No major complaints with the company I'm using - they are Carrier factory authorized, but I have the feeling they aren't the most experienced with these types of issues (they only have two techs). In most cases, I actually like dealing with a small company, but I think they may be in over their head on this one.

Another update, and hopefully we are moving in the right direction. Finally got the Carrier service rep out here, and I was impressed - he definitely seemed to know his stuff.

He said that I need that 4" spacer between the furnace and the N coil. Even though the two are matched sizes, he said that Carrier now recommends that spacer, especially in larger systems (4 ton in my case). He said at hi stage, there really isn't enough room for air to exit the heat exchanger, and then flow into that right leg of the N coil. He said this was now in the CNPVP coil installation instructions (although I couldn't find anything in the instructions that specifically said that).

He acknowledged that I've really had this problem since day 1 (July 2007). I just could never prove it until I did my own BTU calculations.

Out of curiosity, what all kinds of measurements did he take and how long was he there?

I believe, like Mark and others, after reading all your posts that he came to the wrong conclusion.

First he looked at the furnace and coil, and had pretty much concluded that spacer was the problem, but he also talked about moving the txv sensing bulb outside the coil case.

Went outside to check superheat, and although it was < 20 (I think it was about 14F), he said he expects that to be lower - lets put that spacer in. He also verified subcooling was +/- 3 of the required 15F.

He worked out a deal with the HVAC company and agreed to pay for 4 hours of his labor and the cost of the spacer. He did no checks of the compressor and is relying on info passed to him during previous checks.

No his initials were not T H, he's a Carrier Midatlantic rep. Really seemed to know his stuff, gave me his card and email address, so in general he seemed very cooperative and helpful. I won't be too upset if he's wrong. They've gone down a path they can't back out of now (admitting that something is wrong) - they have to keep going until its fixed.

We did talk about that compressor, and the problem with Bristol TS's. He said the real problem with those has been that mechanism that engages the 2nd piston, and since amp draw is going up (although only about 50%), he says that isn't the problem.

OK, another update. 4" spacer installed between the air handler and the N coil evaporator. No difference. And unfortunately, they didn't bring a new compressor.

I'm standing by for round 3.

That was predicitble. Almost pathetic that a mfg rep would even recommend that as a possible solution. Clearly their goal and objective is to admit that the comressor is the problem at all cost.

Funny, we're having the same problem with a large industrial air compressor with motor. issues We're on our 3rd attempt to repair it and finally convinced them to order a different brand motor (the one we should ahve had all along for this application). Some of the fixes probably made hte problem worse. The finger pointing is truely impressive.